This invention relates to combine harvesters and has particular reference to the problems arising from the operation of such machines on ground which is inclined in a fore-and-aft direction of the machines.
As is well known, combine harvesters comprise sieve means to which threshed crop material is passed, the crop material being cleaned while on the sieve means by a fan which operates to blow air through the sieve means so as to render airborne the unwanted material (known as chaff) and impurities such as dust. This allows the thus cleaned grain to pass through the sieve means to a clean grain collecting point for subsequent transfer to a grain tank.
When a combine harvester is operating on ground which is inclined in a fore-and-aft direction of the machine, grain and impurities tend either to accumulate at the front end or to spill over the rear end of the sieve means, depending on whether the machine is experiencing a downward or upward incline, respectively. It is recognized that the amount of air flowing through the sieve means needs to be adjusted according to the nature of the inclination being experienced and U.S. Pat. No. 3,827,442 discloses one method of achieving this objective. The fan of this known arrangement is driven by a variable drive device which is adjusted mechanically according to the nature of the ground inclination, a pendulum being employed for this purpose.
This known arrangement suffers from the fact that it is entirely mechanical and is subject, therefore, to failure due to wear and/or breakage of components or, more importantly, to impaired operation as a result of build-up of dirt, for example, on the components of the linkage system which interconnects the pendulum and the variable drive device. Furthermore, this linkage system is relatively complex and hence expensive. Also the sensitivity of such a mechanical arrangement is not normally impressive.